1. Field of the Invention
The present invention relates to a fuel cell generator.
2. Related Art Statement
A fuel cell generator has recently been remarkably noted as an electricity generator. The fuel cell generator is a system which can directly convert chemical energy of fuel into electric energy, and does not receive a condition of Carnot's cycle, so it has an essentially high energy conversion efficiency, is versatile as to the fuel used (naphtha, natural gas, methanol, coal modified gas, heavy oil and the like), is low in environmental pollution, and its efficiency is not affected by the scale of the electricity generation system, so that the system is an extremely promising technique.
Particularly, a solid electrolyte fuel cell (hereinafter call SOFC for short) is operated at a high temperature of 1000.degree. C., so that an electric reaction is highly active, a noble metal catalyst such as expensive platinum is never required, polarization is small, output voltage is comparatively high, and therefore energy conversion efficiency is remarkably higher than that of other fuel cells. Moreover, since a structural material is all constructed with a solid, the cell has stability and long life.
The SOFC unit consists generally of an air electrode, a solid electrolyte and a fuel electrode. In case of the cylindrical SOFC, a plurality of cylindrical SOFC units are connected in series in such a manner that the fuel electrode of a SOFC unit and the air electrode of an adjacent SOFC unit are connected by means of an interconnector and Ni felt, and also the SOFC units are connected in parallel in such a manner that fuel electrodes of adjacent SOFC units are connected by means of Ni felt.
In the cylindrical SOFC, electrons are received over the whole peripheral surface of the electrode on the interface between the solid electrolyte and the air electrode and on the interface between the solid electrolyte and the fuel electrode. However, the interconnector is only made into contact with the air electrode at one portion, and the Ni felt is made into contact with the fuel electrode at two or three portions for example, so that a generated current flows towards the interconnector and the Ni felt in parallel with the film surface within an air electrode film and a fuel electrode film. However, the air electrode film and the fuel electrode film are thin and have large electrical resistance, so that current loss is large and electricity generating efficiency is lowered. In order to mitigate this electrical resistance and to prevent the voltage loss, it is necessary to make the film thickness thick and to shorten a current passing distance to the interconnector and Ni felt, but a sufficient solution cannot be expected from the limitation in cell structure.